I need a little help on these, i've posted them a few times but i don't get any answers.

Question

29. A common feature of thermal pollution and artificial eutrophication is that they both
a. have sources that are difficult to identify and control
b. cause large mats of algae to bloom in fresh water
c. are a result of power plants and other industrial activity
d. decrease the amount of oxygen dissolved in water

D

33. A true statement about greenhouse gases is that they
a. convert sunlight into eat energy that warms Earth
b. are concentrated in the stratosphere
c. trap hear that is radiated upward from Earth
d. are not affected by human activity

it's either A or C

Answer 1

29. is correct.

Check this site for 33.

http://en.wikipedia.org/wiki/Greenhouse_effect

Answer 2

Right.